Error messages for ? are not great

[brson]

fn main() {
    Ok("lol")?;
}

$ rustc test.rs
error[E0277]: the trait bound `(): std::ops::Carrier` is not satisfied
 --> test.rs:2:5
  |
2 |     Ok("lol")?;
  |     ^^^^^^^^^^ the trait `std::ops::Carrier` is not implemented for `()`
  |
  = note: required by `std::ops::Carrier::from_error`

error: aborting due to previous error

@eddyb says this can be improved by adding #[rustc_on_unimplemented = "the type{Self}cannot be used with?"] to something (maybe the Carrier trait.

crib off of fmt

cc @jonathandturner @nikomatsakis @nrc

[nagisa]

Duplicate of #35946

[steveklabnik]

Yes, and on_unimplemented is in that thread as well.